Compaction roller

ABSTRACT

The invention concerns a soil compaction roller ( 10 ) and a soil compaction machine of which the roller ( 10 ) forms part. The roller ( 10 ) comprises a multi-sided, out-of-round, peripheral compacting surface ( 16 ) which can roll over a soil surface which is to be compacted. The compacting surface ( 16 ) is defined by a series of angularly spaced salient points ( 20 ) and a corresponding series of compacting faces ( 22 ). Each compacting face ( 22 ) is outwardly convex in shape and extends continuously between two adjacent salient points ( 20 ). When the roller ( 10 ) is operative with the compacting surface ( 16 ) rolling over the soil surface, the roller rises up on each salient point ( 20 ) in turn, storing potential energy, and thereafter rolls downwardly onto the succeeding compacting face ( 22 ) to transmit the stored potential energy to the soil surface to compact it. The instantaneous center of rotation of the compacting surface ( 16 ), where it contacts the soil surface during rolling, moves continuously about substantially the full extent of the compacting surface.

BACKGROUND TO THE INVENTION

THIS invention relates to a compaction roller.

Traditionally, soil compaction has been carried out either by means ofround rollers with considerable mass or vibratory rollers. In relativelyrecent times, impact compaction as described in, for instance, thespecification of U.S. Pat. No. 2,909,106, has been used in soilcompaction activities. Impact compactors have been demonstrated toachieve high levels of soil compaction at some depth below the surfacebut in some cases they may not be really effective for compaction oflayer works where a relatively shallow surface zone of the soil mass hasto be compacted. Depending on the soil conditions the impact roller ofan impact compactors may have a tendency merely to disturb the surfacelayer rather than compact it effectively.

The impact roller of a conventional impact compactor may also have atendency to create localised depressions in the soil surface, requiringsubsequent smoothing operations them. They may also generate shock loadsboth on the towing tractor and on the soil mass and can have arelatively low operating speed.

SUMMARY OF THE INVENTION

According to the invention there is provided a soil compaction rollercomprising a multi-sided, out-of-round, peripheral compacting surfacewhich can roll over a soil surface which is to be compacted, thecompacting surface being defined by a plurality of angularly spacedsalient points and a corresponding plurality of compacting faces, eachcompacting face being outwardly convex in shape and extendingcontinuously between two adjacent salient points.

Further according to the invention there is provided a soil compactionroller comprising a multi-sided, out-of-round, peripheral compactingsurface which can roll over a soil surface which is to be compacted andwhich is defined by a plurality of angularly spaced salient points andintermediate compacting faces which are outwardly convex in shape andextend between the salient points, whereby when the roller is operativewith the compacting surface rolling over the soil surface, the rollerrises up on each salient point in turn, storing potential energy, andthereafter rolls downwardly onto the succeeding compacting face totransmit the stored potential energy to the soil surface to compact it,the instantaneous centre of rotation of the compacting surface, where itcontacts the soil surface during rolling, moving continuously aboutsubstantially the full extent of the compacting surface.

The geometry of the roller is preferably such that the salient pointsare equi-angularly spaced about a central axis of the roller and areequidistant from that axis, and each compacting face is symmetricalabout a radial bisector of the two salient points between which thecompacting face extends. The compacting face may be smoothly curved orcomposed of a plurality of flat facets which in combination form anoutwardly convex shape.

Another aspect of the invention provides a soil compaction machinecomprising a soil compaction roller as summarised above. The machine mayhave a pair of the rollers arranged side by side with one another.

In the dual roller configuration there are various possibilities. Forinstance, the soil compaction rollers may be mounted on a common axle inthe manner described for impact compaction rollers in ZA80/2099 (=EP 0017 511). Alternatively the rollers may be suspended independently onseparate axles as described for impact compaction rollers inPCT/IB99/00906. The machine may be self-propelled as described for animpact compaction machine in PCT/GB96/01708 (WO 97/04179), or it mayinclude coupling means for coupling it to a tractive vehicle such as atractor. The machine may also incorporate an auxiliary drive arrangementfor delivering an auxiliary rotary driving force to the rollers asdescribed for a dual roller impact compaction machine in PCT/GB98/01400(WO 98/51866).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a perspective view of a compaction roller according to thisinvention;

FIG. 2 shows a side view of the compaction roller;

FIG. 3 shows an end view of the compaction roller;

FIG. 4 shows a cross-section at the line A—A in FIG. 2; and

FIG. 5 shows a soil compaction machine incorporating two compactionrollers, according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The illustrated multi-sided compaction roller 10 has a central hub 12located on a central axis 14 and a peripheral compacting surface 16which is joined to the hub by radial spokes 18. The compacting surface16 is defined by six salient points 20 which are equi-angularly spacedapart and equidistant from the central axis 14, and six intermediatecompacting faces 22 extending between the salient points. The compactingfaces 22 are identical to one another and each has a smooth, convexcurvature which is symmetrical about a radial bisector of the twosalient points 20 between which it extends. For example, the compactingface 22.1 is symmetrical about the radial bisector 24 of the two salientpoints 20.1.

The salient points 20 and faces 22 of the compaction surface 16 areformed by curved wear plates 26 and 28 respectively which are mounted tothe ends of the spokes 18. The assembly of plates 26 and 28 is stiffenedby ribs 30 which are located at the lateral edges of the plates andwhich are connected to the plates and to the lateral extremities of thespokes 18.

In operation of the compaction roller 10, the hub 12 is mounted on anaxle supported by a carriage which is towed by a suitable towingvehicle, such as a tractor (not shown). In practice, there may be twosimilar compaction rollers arranged side by side. In this case thecompaction rollers may be mounted on a common axle or they may beindependently suspended.

The specification of South African patent ZA 80/2099 (=EP 0 017 511)describes an apparatus in which two impact compaction rollers aremounted side by side on a common axle. A similar mounting arrangementmay be used to mount compaction rollers 10 on a common axle.

PCT/IB99/00906 describes an apparatus in which two impact compactionrollers are suspended independently in a side by side configuration and,once again, a similar mounting arrangement can be used for dualcompaction rollers 10, as shown in FIG. 5.

It is also within the scope of the invention for there to be a singlecompaction roller 10 only, in which case the roller may be mounted inthe manner described in the specification of U.S. Pat. No. 2,909,106.

It is also within the scope of the invention for the compactionroller(s) 10 to form part of a self-propelled machine which may, forinstance, be of the type described in the specification ofPCT/GB96/01708 (WO 97/04179).

EP 0 017 511, PCT/IB99/00906, U.S. Pat. No. 2,909,106 and WO 97/04179describe impact compaction machines in which each compactor mass, as itrolls over a soil surface which is to be compacted, alternately rises upon a salient point, storing potential energy, and then falls forwardlyand downwardly for the stored potential energy to be delivered to thesoil surface as an impact blow by a compaction face which follows thesalient point. As mentioned previously, while this compaction techniquehas been proved to be effective to produce high levels of soilcompaction at considerable depths below the soil surface, they haveseveral disadvantages at least in some applications.

The compaction roller 10 does not act in the manner of an impactcompaction roller. As it rolls over the soil surface, it rises up oneach salient point 20 and then rolls forwardly and downwardly onto thesucceeding compacting face 22. Potential energy which is stored as theroller rises on a salient point is applied to the soil surface as theroller rolls onto the succeeding face 22, but this happens in a farsmoother manner than is the case with an impact compaction roller. Thisis attributable inter alia to the convex shape of the sides 22 whichallows for a smooth transition from each raised, potential energystorage position to a succession of relatively lowered positions as theconvex surface of the following face 22 rolls over the soil surface. Theinstantaneous centre of rotation, i.e. the point at which the compactingsurface 16 makes line contact with the soil surface and about which theroller rotates instantaneously relative to the soil surface, movescontinuously about substantially the full extent of the surface 16.

The action of the roller 10 may be likened to a continuous kneadingaction as opposed to the periodic impact action of an impact compactionroller.

The effect of this is that the soil surface experiences compactingpressure throughout the full rotation of the roller 10, i.e. at allangular positions of the roller. As the roller rises onto a salientpoint 22, the compacting pressure is experienced as a result of thereaction force applied to the soil surface by the roller, and as theroller subsequently rolls forwardly and downwardly onto a compactingface 22, the compacting force is experienced as a result of the storedpotential energy being transmitted to the soil surface.

This action is in contrast to the action of an impact compaction roller.In the case of impact compaction rollers having flat sides, the onlycentres of rotation are at the salient points or corners of the roller.

There is no continuous movement of an instantaneous centre of rotationabout the peripheral compacting surface of the roller. In the case ofimpact compaction rollers having a re-entrant recess between eachsalient point and the subsequent compacting face, the centre of rotationjumps from the salient point to an angularly spaced point on thecompacting face. Hence there is once again no continuous, smooth motionof an instantaneous centre of rotation about the full extent of theperipheral compacting surface.

In contrast to the smooth and continuous application of compactingpressure to the soil surface with the roller 10, both types of impactroller mentioned above apply abrupt, non-continuous pressure spikes tothe soil surface, resulting in disturbance of the soil mass adjacent thesoil surface but often little effective compaction of that mass.

Because of its ability to apply smooth and continuous pressure to thesoil surface, a roller 10, on the other hand, has been demonstrated ininitial tests to have the ability to achieve effective compaction rightto the surface of a soil mass. This makes the roller 10 eminentlysuitable for use in compacting layer-works.

Added to this, the smooth application of compacting pressure with theroller 10 results in a relatively smooth, compacted soil surface. Thisis again in contrast to the operation of an impact compaction roller,where localised indentations are created in the soil surface which mustsubsequently be smoothed, typically by blading.

With the illustrated roller 10 adequate levels of soil compaction canalso be achieved without the substantial shock loads experienced in theoperation of an impact compaction roller. This can in turn lead toreduced wear on the compactor itself and on surrounding equipment andstructures.

A further advantage of the illustrated roller 10, when compared forinstance to impact compaction rollers as seen in the specification of ZA96/6036, arises from the symmetrical shapes of the sides 22 which allowthe roller to be bi-directional, i.e. it can be rotated in eitherdirection over the soil surface, and typically at higher rotationalspeeds than an impact roller, with comparable results. This isparticularly important in cases where rollers 10 are used in areversible, self-propelled machine.

In the preferred roller 10 the compacting faces are smoothly andconvexly curved, but it is within the scope of the invention for thesefaces to be made up of a large number of narrow, flat facets defining,in combination, a generally convex surface.

PCT/GB98/01400 (WO 98/51866) describes an impact compaction machinewhich incorporates an auxiliary drive arrangement to apply an auxiliaryrotary drive to the impact compactor masses or rollers of the machine.This may be necessary when, for instance, the salient points of therollers have a tendency to dig into or slide on the soil surface. Theauxiliary drive arrangement operates to restore the angular velocity ofthe rollers for normal operation to continue. It is also within thescope of the present invention for an auxiliary drive arrangement,similar to that described in WO 98/51866, to be incorporated in thecompaction machine.

Various other modifications are also within the scope of the invention.For instance, while reference has been made to substantially continuousapplication of pressure to the soil surface and substantially continuousmovement of the instantaneous centre of rotation about the full extentof the compacting surface, minor localised deformations, for instancerecesses, in the compacting surface, can be tolerated while stillachieving desirable levels of surface compaction.

1. A soil compaction roller comprising a hub structure defining acentral axis of rotation and a multi-sided, out-of-round, peripheralcompacting surface which has a width measured parallel to the axis andwhich is fixed non-adjustably to an outer periphery of the hub structureso as to be capable of rolling in a direction of rolling over a soilsurface that is to be compacted when the hub structure rotates about thecentral axis, the compacting surface being defined by a plurality ofangularly spaced salient points and an equal plurality of compactingfaces, the salient points being defined at the ends of respective radiiof the roller, each such radius constituting a maximum radius of thecompacting surface and being larger than the maximum radii of thecompacting faces, each compacting face being generally outwardly convexin shape and each generally convex compacting face extending from onesalient point to an adjacent salient point, each salient point extendingparallel to the central axis, the cross-section of each generally convexcompacting face arranged such that an instantaneous center of rotationof each generally convex compacting face, where that generally convexcompacting face contacts the soil surface during rolling, movescontinuously about the full extent of the generally convex compactingface, whereby the roller applies a continuous kneading action to thesoil surface at all angular positions thereof as it rolls over the soilsurface.
 2. A soil compaction roller according to claim 1 whereincompacting faces on either side of each salient point are symmetricalwith respect to one another about a plane containing the central axisand that salient point.
 3. A soil compaction roller according to claim 1wherein each compacting face is symmetrical about an imaginary radialline extending through the compacting face at a location thereofsituated midway between the salient points lying on opposite sides ofthat compacting face.
 4. A soil compaction roller according to claim 3wherein the salient points are equi-angularly spaced about the centralaxis and are equidistant from that axis.
 5. A soil compaction rolleraccording to claim 4 wherein each compacting face is smoothly, convexlycurved.
 6. A soil compaction roller according to claim 4 wherein eachcompacting face comprises a plurality of flat facets which incombination form an outwardly convex shape.
 7. A soil compaction rolleraccording to claim 1 wherein the hub structure comprises a central hub,a plurality of spokes extending outwardly from the central hub, andstiffening ribs carried by the spokes at the periphery of the hubstructure, to which ribs wear plates are mounted.
 8. A soil compactionmachine including a pair of soil compaction rollers mounted side by sidewith one another, each soil compaction roller comprising a hub structuredefining a central axis of rotation, a multi-sided, out-of-round,peripheral compacting surface which has a width measured parallel to theaxis and which is fixed non-adjustably to an outer periphery of the hubstructure so as to be capable of rolling over a soil surface that is tobe compacted when the hub structure rotates about the central axis, thecompacting surface being defined by a plurality of angularly spacedsalient points and an equal plurality of compacting faces, the salientpoints being defined at the ends of respective radii of the roller, eachsuch radius constituting a maximum radius of the compacting surface andbeing larger than the maximum radii of the compacting facts, eachcomposing face being generally outwardly convex in shape and eachgenerally convex compacting face extending continuously from one salientpoint to an adjacent salient point, each salient point extendingparallel to the central axis, the cross-section of each generally convexcompacting surface being constant across a width thereof measuredparallel to the axis and being arranged such that an instantaneouscenter of rotation of each generally convex compacting face, where thatcompacting face contacts the soil surface during rolling, movescontinuously about the full extent of the generally convex compactingface, whereby the roller applies a continuous kneading action to thesoil surface at all annular positions thereof as it rolls over the soilsurface, wherein each compacting face is symmetrical about an imaginaryradial line extending through the compacting face at a location thereofsituated midway between the salient points lying on opposite sides ofthat compacting face.